(a) Field of the Invention
The present invention relates to an automatic focusing device for microscopes utilizing gas such as air.
(b) Description of the Prior Art
As an automatic focusing device for microscopes utilizing gas, there have already known the one disclosed by Japanese published unexamined patent application No. 13293/75. This automatic focusing device is so designed as to inject a gas out of a nozzle fixed to an objective lens of a microscope or formed integrally therewith toward the surface of a specimen and focus the objective lens by moving the objective lens or stage vertically in accordance with pressure of the gas. Speaking more concretely, the automatic focusing device has the construction shown in FIG. 1 in which a microscope tube nozzle 2 is arranged around an objective lens 1 and a gas feed tube 3 is connected to the tube nozzle. The reference numeral 4 represents a revolver, the reference numeral 5 designates a stage and the reference numeral 7 denotes an arm. In the automatic focusing device having such a construction, gas is fed through the gas feed tube 3 into the tube nozzle 2 so that gas passes through space 2a reserved in the tube nozzle 2 and is injected from tip 2b of the nozzle toward the surface of a specimen 6. Pressure of the gas injected in this way is measured with a detector attached to the gas feed tube 3 or the similar member and the objective lens or stage is moved vertically in accordance with the difference between the measured value and a preset value for focusing the objective lens. In case of a microscope equipped with a plural number of objective lenses, however, the conventional automatic focusing device had defects that is requires connective gas tubes to the individual objective lenses and the gas tubes causes hindrance to operation of the microscope since the gas tubes are connected directly to the nozzle or microscope tube nozzle. Further, when the automatic focusing device having the construction shown in FIG. 1 is combined with a microscope equipped with a revolver type objective lens switching device, the individual gas feed tubes are tangled with one another by operating the objective lens switching device, thereby making it impossible to switch the objective lenses in worse cases. In a case where the automatic focusing device is combined with a microscope using an objective lens switching device, it is required to use a single gas feed tube only and switch the objective lenses through tedious procedures of stopping operation of the automatic focusing device, disconnecting the gas feed tube from the objective lens, switching the objective lenses from one to another and thereafter connecting the gas feed tube to the objective lens to be used for microscopy.